This invention relates to a homopolar inductor-alternator synchronous machine and more specifically to a homopolar inductor-alternator synchronous machine constructed to have lower transient or commutating reactances.
Inductor-alternator type machines have both laminated and unlaminated iron in their magnetic circuit structures. Under idealized steady-state balanced conditions, the laminated iron carries both AC and DC fluxes while the unlaminated iron carries only DC flux. The machine field excitation is applied along the unlaminated rotor iron and this iron and the outer unlaminated flux return path (motor frame) form part of the magnetic circuit of the field coil. Under steady-state operating conditions, the magnetic flux wave in the stator travels in synchronism with the rotor, and the reaction flux through the unlaminated iron is DC (not time varying). In a transient condition, the magnetic flux wave is time varying in the rotor, and thus there are time varying armature reaction fluxes which pass through the unlaminated iron parts. These time varying fluxes lead to induced eddy currents in the unlaminated iron, which have two effects: (1) the low conductivity of the iron leads to losses in the machine, (2) the high permeability of the iron causes the inductive reactance to such current flow to be large.
The solid rotor construction of inductor-alternator machines results in good high speed operating characteristics, and the machine is typically operated from a solid state power conditioner. The "on-off" nature of the output waveforms of these conditioners causes the machine to be in a transient state continually. The transient or commutating reactance of the machine when it is used with a power conditioner sets a limit on the power level and frequency of operation of the power conditioner, with a lower transient reactance being desirable. The high reactance of the eddy currents induced in the unlaminated iron sets a lower limit on the commutating reactance which can be achieved.
Conventional methods of reducing commutating reactance such as embedding amortisseur windings in the rotor are not suitable since the rotor pole tip velocity can be in excess of 490 ft./sec. (149 meters/sec.) and the copper windings embedded in the rotor would not withstand the resulting centrifugal forces.
It is an object of the present invention to provide a homopolar inductor-alternator machine having a flux shield for protection against transient fluxes.
It is a further object of the present invention to provide a homopolar inductor-alternator machine lower commutating reactance and losses.